1. Field of the Invention
The present invention is directed to an acceleration sensor (accelerometer), preferably of silicon, of the type which can be manufactured using micromechanical manufacturing methods.
2. Description of the Prior Art
Extremely small and thus economical micromechanical acceleration sensors for acceleration measurements in the range of accelerations due to gravity require electronic circuits for the evaluation of the measured result. Such sensors are usually manufactured in a hybrid structure because a realization of the sensor and the circuit in the same substrate requires an additive manufacturing technology. The electronic circuit and the micromechanical sensor thus are successively manufactured. An improvement of the manufacturing method is thus achieved due to an integration of the method for manufacturing the sensor with the manufacturing method of the electronic components in order to thus obtain a sensor integrated on a chip with the circuit. An extremely economical method for manufacturing such integrated micromechanical systems arises from the simultaneous employment of the manufactured layers, for example of silicon, for the electronic part as well as for the micromechanical part, i.e., the mass part suspended from springs (resilient elements). For example, the deposition of a layer of polysilicon as a gate electrode in the circuit can be employed simultaneously as the layer from which the micromechanical component parts, i.e., particularly the mass part, are structured. One problem thereby arising is that the relatively thin layer provided for the electrodes of the electronic components constitutes an extremely thin movable, mechanical part. The mass part provided for the acceleration sensor, the size of the acceleration to be determined from the inertia of this mass part, will therefore not comprise adequate mechanical stability. This factor also results in the sensor having its highest sensitivity in a direction perpendicular to the substrate surface. Although in theory one could stabilize the mass part in this direction on the basis of appropriately fashioned spring from which the mass part is suspended, this could not be accomplished within the limited resolution of the lithography employed in the manufacture of these types of products. The spring-like supports manufactured in the layer provided for the structuring of the mass part, from which the mass part is suspended, cannot be manufactured so narrow that the lateral expanse is less than their vertical expanse. The mass part can therefore oscillate more easily in the direction perpendicular to the substrate than in the substrate plane. It is necessary in many applications such as, for example, navigation systems on a chip, to have an oscillatory system wherein an influence of inertial forces on the mass part causes primarily an excursion (displacement) of the mass part in the substrate plane. It is also necessary to be able to register the excursion of the mass part; this can ensue, for example, by measuring a change in the respective capacitances of capacitors formed of electrodes immovably arranged relative to the substrate or relative to the mass part.